It is proposed that Raman and Fourier transform infrared spectroscopy be applied to investigate the molecular mechanisms of light detection in normal and abnormal vision. It has been shown in a preliminary report (Rothschild et al. Science 191:1176 (1976) that the structure of photoreceptor membrane including the ospin protein membrane lipids and retinylidene chromophore can be probed by using these techniques. Studies will also be made on oriented films made from purple membrane fragments. The membrane protein in purple membrane, bacteriorhodopsin, has been shown to act as a light driven proton pump. Fourier transform infrared spectroscopy and resonance Raman spectroscopy on oriented purple membrane films may reveal details of the conformational changes occurring in bacteriorhodopsin during proton translocation.